1. Field of the Invention
The present invention relates to a vibration gyroscope and a method for adjusting the characteristics of the same, and more particularly, to a vibration gyroscope having a detecting device for obtaining a signal corresponding to a rotation angular velocity and a method for adjusting the characteristics of the same.
2. Description of the Related Art
FIG. 6 is a diagram showing an example of a conventional vibration gyroscope. A vibration gyroscope 1 shown in FIG. 6 includes a vibrator 2. The vibrator 2 includes a vibration member 3 having a regular triangular prism shape. The vibration member 3 is made from, for example, permanently elastic metal materials such as elinvar. At nearly the centers of the three side faces of the vibration member 3, three piezoelectric elements 4a, 4b, and 4c are formed, respectively. These piezoelectric elements 4a to 4c each include a piezoelectric layer made up of ceramic. Each piezoelectric element is provided with electrodes at both primary surfaces of the piezoelectric layer. One electrode on a primary surface of the piezoelectric layer is adhered to a side face of the vibration member and the other electrode, which is disposed on the other primary surface of the piezoelectric layer, is used for signal input and output.
In the vibrator 2, two piezoelectric elements 4a and 4b are used for feedback and detection, and the other piezoelectric element 4c is used for driving. Two piezoelectric elements 4a and 4b are connected to the input terminal of an oscillation circuit 6 through resistors 5a and 5b which serve as the loads of the piezoelectric elements. In this case, to use the vibration gyroscope with the highest synchronous-detection efficiency, the impedances of the resistors 5a and 5b are set equal to the impedances of piezoelectric element 4a and 4b, which serve as detecting elements, in a matching condition, respectively. The impedance Z of a piezoelectric element in a matching condition is expressed by Z=1/(2.pi.fC), where f indicates the frequency of a driving signal and C indicates the capacitance of the piezoelectric element. The output terminal of the oscillation circuit 6 is connected to piezoelectric element 4c. Piezoelectric elements 4a and 4b are connected to the non-inverting input terminal and the inverting input terminal of a differential amplifier circuit 7, respectively. The output terminal of the differential amplifier circuit 7 is connected to the input terminal of a synchronous-detection circuit 8. The output terminal of the synchronous-detection circuit 8 is connected to the input terminal of a smoothing circuit 9.
When a driving signal output from the oscillation circuit 6 is applied to piezoelectric element 4c in the vibration gyroscope 1 shown in FIG. 6, the vibration member 3 vibrates in the direction perpendicular to the primary surfaces of piezoelectric element 4c. When the vibration gyroscope 1 rotates about the axis of the vibration member 3 in this state, the direction of vibration of the vibration member 3 changes due to the Coriolis force. Then, a signal according to the rotation angular velocity is generated between the piezoelectric elements 4a and 4b. This signal is detected by the differential amplifier circuit 7. The signal output from the differential amplifier circuit 7 is synchronously detected by the synchronous-detection circuit 8, and the output signal of the synchronous-detection circuit 8 is smoothed by the smoothing circuit 9. Therefore, the rotation angular velocity is detected from the output signal of the smoothing circuit 9 in this vibration gyroscope 1.
In the vibration gyroscope 1 shown in FIG. 6, the relationship between temperature and sensitivity change rate without any compensation are determined by the temperature characteristics of the ceramic in the piezoelectric layers of piezoelectric elements 4a and 4b, which serve as detecting elements. To obtain the desired relationship between temperature and sensitivity change rate, the level of a driving signal is changed with the use of a thermistor or diode in a driving-signal processing system including the oscillation circuit 6. Alternatively, the gain of a detected signal is changed with the use of a thermistor or diode in a detected-signal processing system including the differential amplifier circuit 7, the synchronous-detection circuit 8, and the smoothing circuit 9. When a thermistor or diode is used, however, the cost of the vibration gyroscope increases due to high cost of the thermistor or diode, and the number of used components also increases.
To improve the response of the vibration gyroscope 1 shown in FIG. 6, the vibration frequency of the vibrator is increased or the vibrator material is changed. However, to increase the vibration frequency of the vibrator, the size and the shape of the vibrator need to be changed and changes of the circuit constants in the peripheral circuits are also required. These factors cause high cost. To change the vibrator material, the vibrator needs to be changed and changes of the circuit constants in the peripheral circuits are also required. These factors also increase cost.